Waste, refuse or garbage can be fully or partly decomposed by a thermal degradation treatment utilizing a reaction chamber to which the waste material is supplied, to which air is fed for reaction with the waste material, and which is followed by a waste heat boiler which recovers heat from the gases produced.
In such apparatus, the waste material undergoes pyrolysis, destructive distillation or carbonization, or combustion.
The reaction products are generally partly gas and partly solid residues like ash, carbonized products or partly carbonized products. To achieve the greatest possible degree of reaction of the waste material, the maintenance of a reaction temperature sufficient for the reaction is important. The heat raising the temperature of the incoming waste stream from the inlet temperature to the reaction temperature and the heat required for the decomposition reaction primarily derives from the waste stream itself and as a rule the supply of additional energy is not necessary.
However, there are phases in the operation of such apparatus when the amount of heat liberated by the reaction is too small for maintaining the requisite reaction temperature. In such unfavorable operating conditions, external energy must be supplied. In the past, the supply of external energy has been accomplished by providing the apparatus with one or more burners, so called support burners, utilizing commercially available fuel. Such fuel could be solid fuels, for example coal, combustible liquids, for example fuel oil, or combustible gases, for example methane.
As a rule as well, when such burners are used, they are also supplied with the requisite oxygen, usually in the form of combustion air. The supply of air can be effected in an air excess which is desirable for decomposing the waste stream. However, support burners of this type require the use of relatively expensive fossil fuels.
The waste stream to be decomposed is highly heterogeneous. It is usually composed of combustible materials, water and uncombustible or only partly combustible materials, such that the heat value of the waste stream fluctuates greatly. It is known to use a waste fraction which has a high heat value by separating it from the waste and processing it to granules.